This invention relates to a valve having a rocker and an isolation diaphragm for alternately sealing one or the other of two fluid inlet or outlet ports. More specifically, this invention deals with a rocker valve suitable for selectively sealing ports of relatively large diameter.
It is known in the art to employ a rocker in a three-way valve having a single fluid inlet port and two outlet ports. In such valves, the rocker pivots between two extreme positions at which a valve sealing member mounted on the end of a pressure arm of the rocker closes one or the other of the outlet ports, the inlet port being constantly open.
Because of the arcuate motion of the valve rocker as it rotates about its pivot axis, the angle between the plane of the sealing surface of each valve sealing member on one of the rocker pressure arms relative to the plane of the valve seat surrounding the outlet port which is to be sealed varies as each respective valve sealing member approaches its corresponding valve seat. In order to minimize the problem of uneven seating caused by having a rotating rocker engage against a planar valve seat, the diameter of the arc of travel of the rocker must be relatively large in comparison with the diameters of the valve seat openings. Where larger port openings are required, the rocker must be of correspondingly greater size. As the size of the rocker increases, the force necessary to move it also increases due to be enlarged area of the rocker which is exposed to fluid pressure.
Moreover, even in valves with relatively large rockers, after initial engagement of a valve sealing member against its respective valve seat, the resilient nature of the interface between the valve sealing member and valve seat allows for movement of the valve sealing member against the valve seat causing relative skewing between the sealing member and valve seat until the rocker reaches a terminal position. The terminal position of the rocker with respect to the valve seat can vary depending on dimensional tolerances, resiliency of elastomeric sealing elements, and normal wear in use.
A valve of the aforesaid type is disclosed in U.S. Pat. No. 5,199,462 to Baker for a Valve Having Rocker Valve Sealing Member and Isolation Diaphragm. Although the invention of this patent admirably overcomes certain leakage problems associated with prior art valves, the angular movement of the sealing members on this valve and the other prior art valves upon which it improves causes the valve to suffer from the shortcomings discussed above when used to seal valve seats on ports of relatively large diameter.